| 1. |
- Derba-Maceluch, Marta, et al.
(författare)
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Suppression of xylan endotransglycosylase PtxtXyn10A affects cellulose microfibril angle in secondary wall in aspen wood
- 2015
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 205:2, s. 666-681
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Tidskriftsartikel (refereegranskat)abstract
- Certain xylanases from family GH10 are highly expressed during secondary wall deposition, but their function is unknown. We carried out functional analyses of the secondary-wall specific PtxtXyn10A in hybrid aspen (Populus tremulaxtremuloides).PtxtXyn10A function was analysed by expression studies, overexpression in Arabidopsis protoplasts and by downregulation in aspen.PtxtXyn10A overexpression in Arabidopsis protoplasts resulted in increased xylan endotransglycosylation rather than hydrolysis. In aspen, the enzyme was found to be proteolytically processed to a 68kDa peptide and residing in cell walls. Its downregulation resulted in a corresponding decrease in xylan endotransglycosylase activity and no change in xylanase activity. This did not alter xylan molecular weight or its branching pattern but affected the cellulose-microfibril angle in wood fibres, increased primary growth (stem elongation, leaf formation and enlargement) and reduced the tendency to form tension wood. Transcriptomes of transgenic plants showed downregulation of tension wood related genes and changes in stress-responsive genes. The data indicate that PtxtXyn10A acts as a xylan endotransglycosylase and its main function is to release tensional stresses arising during secondary wall deposition. Furthermore, they suggest that regulation of stresses in secondary walls plays a vital role in plant development.
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| 2. |
- Abramsson, Alexandra, 1973, et al.
(författare)
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Defective N-sulfation of heparan sulfate proteoglycans limits PDGF-BB binding and pericyte recruitment in vascular development
- 2007
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Ingår i: GENES & DEVELOPMENT. - : Cold Spring Harbor Laboratory. - 0890-9369 .- 1549-5477. ; 21:3, s. 316-331
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Tidskriftsartikel (refereegranskat)abstract
- During vascular development, endothelial platelet-derived growth factor B (PDGF-B) is critical for pericyte recruitment. Deletion of the conserved C-terminal heparin-binding motif impairs PDGF-BB retention and pericyte recruitment in vivo, suggesting a potential role for heparan sulfate (HS) in PDGF-BB function during vascular development. We studied the participation of HS chains in pericyte recruitment using two mouse models with altered HS biosynthesis. Reduction of N-sulfation due to deficiency in N-deacetylase/N-sulfotransferase-1 attenuated PDGF-BB binding in vitro, and led to pericyte detachment and delayed pericyte migration in vivo. Reduced N-sulfation also impaired PDGF-BB signaling and directed cell migration, but not proliferation. In contrast, HS from glucuronyl C5-epimerase mutants, which is extensively N- and 6-O-sulfated, but lacks 2-O-sulfated L-iduronic acid residues, retained PDGF-BB in vitro, and pericyte recruitment in vivo was only transiently delayed. These observations were supported by in vitro characterization of the structural features in HS important for PDGF-BB binding. We conclude that pericyte recruitment requires HS with sufficiently extended and appropriately spaced N-sulfated domains to retain PDGF-BB and activate PDGF receptor β (PDGFRβ) signaling, whereas the detailed sequence of monosaccharide and sulfate residues does not appear to be important for this interaction.
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| 3. |
- Busse, Marta, et al.
(författare)
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Contribution of EXT1, EXT2, and EXTL3 to heparan sulfate chain elongation
- 2007
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 282:45, s. 32802-32810
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Tidskriftsartikel (refereegranskat)abstract
- The exostosin (EXT) family of genes encodes glycosyltransferases involved in heparan sulfate biosynthesis. Five human members of this family have been cloned to date: EXT1, EXT2, EXTL1, EXTL2, and EXTL3. EXT1 and EXT2 are believed to form a Golgi-located hetero-oligomeric complex that catalyzes the chain elongation step in heparan sulfate biosynthesis, whereas the EXTL proteins exhibit overlapping glycosyl-transferase activities in vitro, so that it is not apparent what reactions they catalyze in vivo. We used gene-silencing strategies to investigate the roles of EXT1, EXT2, and EXTL3 in heparan sulfate chain elongation. Small interfering RNAs (siRNAs) directed against the human EXT1, EXT2, or EXTL3 mRNAs were introduced into human embryonic kidney 293 cells. Compared with cells transfected with control siRNA, those transfected with EXT1 or EXT2 siRNA synthesized shorter heparan sulfate chains, and those transfected with EXTL3 siRNA synthesized longer chains. We also generated human cell lines overexpressing the EXT proteins. Overexpression of EXT1 resulted in increased HS chain length, which was even more pronounced in cells coexpressing EXT2, whereas overexpression of EXT2 alone had no detectable effect on heparan sulfate chain elongation. Mutations in either EXT1 or EXT2 are associated with hereditary multiple exostoses, a human disorder characterized by the formation of cartilage-capped bony outgrowths at the epiphyseal growth plates. To further investigate the role of EXT2, we generated human cell lines overexpressing mutant EXT2. One of the mutations, EXT2-Y419X, resulted in a truncated protein. Interestingly, the capacity of wild type EXT2 to enhance HS chain length together with EXT1 was not shared by the EXT2-Y419X mutant.
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| 4. |
- Busse, Marta, 1976-
(författare)
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EXT Proteins in Heparan Sulfate Biosynthesis
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heparan sulfate (HS) is a long unbranched polysaccharide composed of alternating glucosamine and hexuronic (glucuronic or iduronic) acid residues. Modification by sulfate groups in various positions generates a highly heterogeneous molecule. HS is synthesized as a proteoglycan by virtually all cells, and play pivotal functions in signaling and developmental patterning, but also in pathogenic events such as tumor metastasis and microbial adhesion.This thesis deals with the properties of enzymes involved in HS chain elongation. Polymerization of the HS chain is believed to be catalyzed by the EXT family of proteins. In humans, the EXT family consists of five members: EXT1, EXT2, EXTL1, EXTL2 and EXTL3; their respective functions in HS biosynthesis are not fully understood. In this study, for the first time, successful in vitro HS polymerization on oligosaccharide acceptor substrates was demonstrated, using recombinant EXT1 and EXT1/EXT2 complex. EXT1 formed longer chains than EXT1/EXT2 and their mechanisms of sugar incorporation were different. Suppression of EXT1 or EXT2 expression by siRNA in a human cell line resulted in reduction of HS chain length. In contrast, cells transfected with EXTL3 siRNA produced longer HS chains. Overexpression of soluble EXT1, alone or co-expressed with EXT2, resulted in increased chain length, whereas overexpression of soluble EXT2 or EXTL3 has no detectable effect on HS chain elongation. Structural analysis of HS from fibroblasts isolated from mice with a hypomorphic mutation in Ext1 showed that they produced significantly shorter HS chains then the wild-type fibroblasts (20 and 70 kDa, respectively). The disaccharide composition of the HS produced by the mutant cells was virtually indistinguishable from that of the wild-type HS, however, the mutant HS chains contained higher proportions of unmodified regions. Mutant cells responded less efficiently than wild-type cells to low concentrations of FGF2, as analyzed by ERK phosphorylation assay.
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| 8. |
- Hedenström, Anders, et al.
(författare)
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Bat flight generates complex aerodynamic tracks
- 2007
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 316:5826, s. 894-897
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Tidskriftsartikel (refereegranskat)abstract
- The flapping flight of animals generates an aerodynamic footprint as a time-varying vortex wake in which the rate of momentum change represents the aerodynamic force. We showed that the wakes of a small bat species differ from those of birds in some important respects. In our bats, each wing generated its own vortex loop. Also, at moderate and high flight speeds, the circulation on the outer ( hand) wing and the arm wing differed in sign during the upstroke, resulting in negative lift on the hand wing and positive lift on the arm wing. Our interpretations of the unsteady aerodynamic performance and function of membranous-winged, flapping flight should change modeling strategies for the study of equivalent natural and engineered flying devices.
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| 9. |
- Johansson, Christoffer, et al.
(författare)
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The near and far wake of Pallas' long tongued bat (Glossophaga soricina).
- 2008
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 211:Pt 18, s. 2909-2918
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Tidskriftsartikel (refereegranskat)abstract
- The wake structures of a bat in flight have a number of characteristics not associated with any of the bird species studied to this point. Unique features include discrete vortex rings generating negative lift at the end of the upstroke at medium and high speeds, each wing generating its own vortex loop, and a systematic variation in the circulation of the start and stop vortices along the wingspan, with increasing strength towards the wing tips. Here we analyse in further detail some previously published data from quantitative measurements of the wake behind a small bat species flying at speeds ranging from 1.5 to 7 m s(-1) in a wind tunnel. The data are extended to include both near- and far-wake measurements. The near-/far-wake comparisons show that although the measured peak vorticity of the start and stop vortices decreases with increasing downstream distance from the wing, the total circulation remains approximately constant. As the wake evolves, the diffuse stop vortex shed at the inner wing forms a more concentrated vortex in the far wake. Taken together, the results show that studying the far wake, which has been the standard procedure, nevertheless risks missing details of the wake. Although study of the far wake alone can lead to the misinterpretation of the wake topology, the net, overall circulation of the main wake vortices can be preserved so that approximate momentum balance calculations are not unreasonable within the inevitably large experimental uncertainties.
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